About Chris KP
The Science of Stuff
Chris' Twitter feed
News and Musings
Corporate Presentations

Floating Mice

In what has to make one’s inner sci-fi nerd stir excitedly, NASA has announced research that involved makingImage by be_khe and kukkurovaca mice levitate. In the past researchers in several countries managed to levitate insects, small lumps of solid matter and globs of liquid in ultrasonic fields, but Yuanming Liu and his team at NASA's Jet Propulsion Laboratory used a strong magnetic field.

Under normal conditions we don’t notice any effects of magnets on living tissues.  Of course that doesn’t mean that there are no effects.

Most naturally occurring materials will show some level of “diamagnetism” – a repelling response to an applied magnetic field. There is a great deal of water in living tissue, including that in mice (and humans, of course, which is one of the reasons MRI technology works, but that’s another story). When inside a magnetic field, water molecules exhibit diamagnetism, pushing against the field. If enough water molecules do this at once, and they are contained, the container – in this case a mouse’s body – can be made to levitate.

Apparently the mice weren’t very happy being levitated and needed to be tranquilised so they didn’t end up spinning around and around as they tried to find something to grab onto. Fair enough – it has to be a pretty weird sensation.

I’m now wondering if this could be sized up and reversed to produce the kind of artificial gravity of the sort that is featured in so many movies – very cool.


If you do what your dentist tells you, you’ll brush your teeth at least twice a day. I do, and – like most people I use toothpaste. The other day I found myself reading the ingredients and it was quite a list. That got me thinking about the very nature of toothpaste, a substance that – to do its job – must exhibit a wide range of characteristics. So I’ve compiled a list of common toothpaste ingredients and what they do. I also stumbled upon an explanation for why the orange juice you drink after brushing your teeth tastes so foul.

You need to be able to store toothpaste in a small space (eg a tube) but spread it around a larger space (ie your mouth)
Sodium lauryl sulphate (SLS) (AKA Sodium dodecyl sulfate (SDS)) is a surfactant used in a wide variety of products including floor cleaners, shampoos, shaving foams, engine degreasers and bubble baths. In toothpaste it is used primarily as a foaming agent.

Glycerin (AKA glycerol) is a sugar alcohol. It is sweet and viscous so it’s partly there for consistency and partly for flavour.

Carrageenan is any of a family of linear sulphated polysaccharides and is used as a stabilizer, added to prevent constituents separating. Carrageenan is derived from red seaweed (Chondrus crispus) and it is a non-Newtonian fluid, specifically it is thin under shear stress and recovers its viscosity once the stress is removed. This is one reason that toothpaste is easy to squeeze out of the tube, and holds its shape somewhat when outside afterwards, but does not easily drip out of the tube if the lid is left off.

It needs to remove things that are stuck to your teeth

Hydrated silica is a form of silicon dioxide, which has a variable amount of water in the formula. It is also known as silicic acid, a term usually used for its form dissolved in water. It is found in nature, as opal, which has been mined as a gemstone for centuries and in the cell walls of diatoms. It’s used as mild abrasive (this is why toothpaste is sometimes recommended for repairing minor scratches in glass.

Mica refers to silicate minerals (which contain silica, SiO4). They are sometimes called “sheet silicates” because they form a sheet-like crystalline structure. Like
hydrated silica, mica acts as a mild abrasive to aid polishing of the tooth surface. It also adds a glittery shimmer to the paste.

Ideally it should make your teeth stronger and if possible cleaner looking
Sodium fluoride is used to enhance the strength of teeth by the formation of fluoroapatite, a naturally occurring component of tooth enamel. In theory this strengthens teeth to prevent cavities.       

Titanium dioxide is used to provide whiteness and opacity.

It should taste nice
Sodium saccharin is the sodium salt version of saccharin (AKA benzoic sulfinide). It is in toothpaste for flavour and is hundreds of times sweeter than sucrose.

See also glycerin, above.

Sorbitol (AKA Glucitol) is another sugar alcohol.

It should discourage the presence and growth of disease-causing organisms

Triclosan (AKA 5-chloro-2-(2,4-dichlorophenoxy)phenol) is a potent wide spectrum antibacterial and antifungal agent.

As for why drinking orange juice after brushing your teeth is so unpleasant, it’s almost certainly has nothing to do with the minty flavour of the toothpaste. Apparently the same unpleasant taste is experienced if you use toothpaste of any flavour (and there are loads of flavours out there), and in other contexts mint and citrus can be a very pleasant combination. It seems that sodium lauryl sulphate might hold the secret, because SLS does more than just help toothpaste lather. SLS also suppresses your sweet receptors, so basically when you drink the orange juice you can taste all the various components of the flavour, except the sweet bits.


Is there an "i" in "robot"?

Photo by FlySiIn 1942 Isaac Asimov introduced the world to his 3 laws of robotics. These laws are primarily designed to ensure that a robot remains subservient to humans and that it never hurts a human. The laws also demand that a robot protect itself and in this respect it seems that if robots are in conflict with each other, they do what people often do – they cheat, they deceive and they get very selfish.

Asimov’s laws are as follows:

1. A robot may not injure a human being or, through inaction, allow a human being to come to harm.
2. A robot must obey any orders given to it by human beings, except where such orders would conflict with the First Law.
3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

Recent research out of Switzerland has shown that when they are allowed to evolve, robots will indeed protect themselves, as the third law requires, and that they will do this at the expense of other robots if necessary.

Working at Ecole Polytechnique Fédérale of Lausanne, Dario Floreano, Laurent Keller and PhD student Sara Mitri placed their robots in an arena with a light ring marked near one end and a dark ring marked near the other. The light-coloured ring was a “good resource” and the dark-coloured ring was “poisonous”. The robots were able to sense the different rings and when they found the good resourse they would received points. Other robots could sense this light and would be attracted to the same area. If the robots stayed near the poisoned region they were penalised points. There were 1,000 robots in the experiment, and while each robot had the same hardware and much of the same programming, each one had a unique 264-bit binary code or "genome". In addition, the robots had a blue light that would randomly flash and could be detected by the other robots.

The robots were effectively competing for access to the good resource ring and after the first tests, the highest-scoring 200 robots were selected for the next phase. Each of these 200 robots had its genome mutated (with a 1 in 100 chance that any bit would be changed) and was “mated” with another robot in order to mix the various sections of their programs. This produced a new generation of robots. This new generation (and subsequent generations) were better at finding the good resource, partly because they were increasingly drawn to clusters of randomly flashing blue light from other robots who had found the light ring. Of course there is only limited space around this ring and once the researchers allowed the flashing of the blue light to evolve with the rest of the genome, an interesting change began to emerge – the robots were still able to find the good resource, but they were more selective about when they shone their blue light. By the 50th generation, they would still use the blue light in neutral parts of the arena, but they were much less likely to shine the light once they had found the good resource.

After 500 generations, 60 percent of the robots had evolved to keep their light off when they found the good resource. In this way they reduced the risk of other robots crowding in on the good resource – apparently they were hogging it all for themselves. Some of the robots even appeared to become somewhat paranoid; they evolved to move away from another robot’s blue light, as if they did not want to share anything with the other robot (or that the other robot would not share with them) or that they simply trust the messages from other robot.

This experiment was a case of “each robot for himself”, but it would be interesting to see how cooperative the robots might evolve to be if collaboration or group success was valued. For example, what would happen if the robots were awarded points when other robots detected their light and joined them. In another possible extension you could try different “species” of robots, some as “predators” and some as “prey” – could “predators” evolve to hunt in packs, or select the “weaker” individual at the back of a herd or “prey”? Would “prey” robots evolve to be less detectable or more protective of each other? I’m sure Floreano, Keller and Mitri will be having the same thoughts, and presumably telling each other . . .

Never Forget a Face

Scientists from the University of Washington have a warning for you: if you’ve ever upset a crow, watch out. There’s every chance that the crow will be out for revenge when next you cross paths, although a Dick Cheney mask might help. 

Everybody knows that when scientists catch wild animals for tagging and monitoring, etc it’s for their own good. At least it’s for the good of their species. More broadly it’s for the good of all of us, as we try to advance our understanding of the relationships between living things in all their labyrinthine complexity.

Of course the subjects of these studies might not see it that way. When a group of large bipedal creatures grab you and attach a weird little tag on you, it might seem rather more sinister and frightening. You’d be forgiven for taking it pretty badly. You might even hold a grudge about it, and you wouldn’t be alone.

For some time, many researchers have suspected that some birds have the ability to recognise and remember individual faces. John Marzluff and colleagues at the University of Washington have produced compelling evidence of exactly that trait. Marzluff asked his team to wear rubber “caveman” masks, which he called “dangerous” masks while trapping and banding crows on the university’s campus in Seattle. Crows don’t like being trapped and banded, and in the weeks and months that followed researchers and volunteers wore the dangerous masks while walking around campus and the crows kicked up a right fuss whenever anyone in such a mask came near.

In order to check that this behaviour was not simply a response to the unnatural rubbery countenance of the masks, Marzluff asked people to walk about the campus wearing different “neutral” masks, specifically Dick Cheney masks. The crows remained utterly calm when confronted by one of the Dick masks. Apparently if Dick Cheney wants to be liked (or at least ignored) he needs to hang around with people even less popular than himself. Maybe he has been.

Crows are very responsive to other crow behaviour and they learn from the reactions of other crows. In the years - yes years – that follow initial tagging, crows lose none of their memory or their animosity, and they don’t keep it to themselves. Marzluff, co-author of In the Company of Crows and Ravens, explained that he was “scolded” by 47 of the 53 crows he came across while wearing a dangerous mask. Only seven of these had been banded in the original trapping and banding. Marzluff and his team believe that crows learn from their parents and other crows in their flock how to recognise threatening humans from less threatening ones. And it wasn’t just him; he deliberately arranged for a wide variety of people to wear the masks in order to ensure that it was the masks – or rather the faces – that the crows were recognising. Tall people, short people, men, women, old people, young people, bald people, people in hats.

Apparently crows are much better at recognising faces than humans are and there’s a fun test to prove this at www.npr.org/templates/story/story.php?storyId=106826971

So if you’re looking for a novel “trick” when trick or treating, you could do worse than taking the time to make masks identical to your unfavoured neighbour face and hassling some crows outside their house.

Do you hear what I see?

Despite a previous entry, I’m not obsessed with the human sense of hearing. However, I did come across some interesting research that (eventually) lead to this story, which I shared with listeners of ‘Einstein-A-Go-Go’ a couple of weeks ago.Photo by Rob Parkin

The phrase “echolocation” was first coined in 1944 by Donald Griffin (Harvard University), while he was investigating the navigational behaviour of bats. Of course bats are not the only animals to use this technique. Toothed whales (such as dolphins, porpoises, orcas and sperm whales) also use echolocation, as some birds, shrews and tenrecs. Some of the sounds are at frequencies that are audible to humans and some are not, but that’s ok – they’re not usually talking to us.

The idea of echolocation is that the animal makes a sound; if the sound waves collide with an object, they will bounce back (or echo) and are detected by the animal. The delay between when the sound is emitted and the detection of an echo indicates the distance of an object. Animals that use echolocation may emit sounds from their mouths, or from specialised organs in the nose or head (I especially like the “melon” that features in the head of toothed whales).

Technologically, the human equivalent of echolocation is SONAR (SOund NAvigation and Ranging), used most notably by submarines. The first active SONAR systems were developed by 1918. So interestingly, the development of SONAR preceded the discovery of echolocation by humans, but as is often the case, nature had got there first.

The evolution of echolocation has had some interesting twists. In 2008 Nancy Simmons et al published research (Nature 451, 818-821) showing that the earliest known bats did not have the morphological hardware to echolocate and that they probably developed the ability to fly first. Presumably they were able to sense the environment around them using passive audio signals as well as visual and olfactory ones. Either that or they simply flew into things a lot.

Some humans have learnt to use echolocation as well. Daniel Kish is probably the best known case. Daniel is lead founder and CEO of World Access for the Blind, and trains other blind people to use echolocation.

Now a team of Spanish researchers believe they have developed a series of tests to help unlock other human’s echolocation abilities. Juan Antonio Martínez says that in a couple of hours a day for a few weeks anyone can learn how to echolocate using clicks. Martinez and his colleagues had their paper published in Acta Acustica united with Acustica. As well as aiding the blind, these techniques could also be useful for emergency workers operating in dark or obscured situations such as those encountered by firemen and rescue workers.

I’ve tried this a few times and it’s not easy, but you start to sense how it would work. I’m kind of looking forward to the next power blackout . . .